Electric-motor control for feed mechanisms



' Nov. 8, 1927.

. 1,648,680 R. D. GIVEN ELECTRIC MOTOR CONTROL FOR FEED MECHANISMS Filed Jan. 29. 1927 Invent or Ralph D. Given,

His Attor-ney Patented Nov. 8, 1927.

UNITED STATES PATENT OFFICE.

RALPH D. GIVEN, OF LEAMING'I'ON, ZEN GLAND, ASSIGNOR TO GENERAL ELECTRIC CO!- PANY, A CORPORATION OF NEW YORK.

ELECTRIC-ROTOR CONTROIi FOR FEED MECHANISMS.

Application filed January 29, 1927, Serial No. 164,612, and in Great Britain February 9, 1928.

The present invention relates to animproved system of electric motor control, particularly adapted fo the operating conditions which obtain in the feed control of magazine, continuous type, grinders, which are used in the preparation of wood pulp for paper making although not limited to such machines. The electrical equipment of such a machine usually consists of a main motor driving the grindstone, and a feed motor driving chains which force the logs of wood down the magazine on to the stone.

It is also usual to provide control gear to vary automatically the speed of the feed motor according to changes in the load on the main motor, so that the output is maintained practically constant, the feed motor being stopped in the case of excessive overload.

It has been found in practice that the stones will not sustain large overloads with; out injury or fracture, so that the overload protective device must be set low, and further that the logs are very liable to pack in the magazine causing frequent and severe overloads on the feed motor. The result is frequent interruptions in grinding, and if these are due to packing the feed motors have to be reversed for a short time to relieve the packed condition of the logs before grinding can be restarted.

The object of the present invention 1s to improve the operation by arranging that the overload due to either excess pressure on the stones or packing of the logs, instead'of stopping the feed motor, reverses it under time limit control to relieve the overload and then runs it forward again to continue grinding. The settin of the time limit is not important, as if t e overload is not entirely cleared when the motor tries to run forward, the overload will trip again and reverse the motor for a second period, and so on until grinding can be continued. I also provide a separate overload relay to protect the feed ,motor when running reversed, and this can be set high, as there is no danger of injuring the stone in this case, and the full overload capacity of the motor can be used to clear the jam.

Further, I provide a change-over switch so that the time limit relay and the low-set Qhalf casing raise and giving reverse rotation.

chains stationary and running the feed motors, which being mounted on the top lower the casing up and down the chainsa The accompanying diagram illustrates one method of carrying this invention into effect. Only those control devices relevant to the features of control being described are shown, it being'understood that a complete equipment would include several other additional features. It should also be understood that the scheme applies equally to doublestone grinders, i. e., where two stones are coupled, one each end, to one main motor, in which case there are two feed motors and these would-be supplied with separate control gear so that each feed motor would clear itself of overloads as described above independently of the other.

In the diagram 1 represents the main motor driving the stone 2. The feed motor 3 shown as a shunt wound direct current machine drives. the chains 4 throu h gearmg 5. There will be one pair of 0 sins on two opposite sides of the magazine 6, both pairs being driven by the feed motor. The 5 shunt field of the motor with rheostat 7 in. circuit is energized from constant voltage I bus bars 8. The feed motor has reversing contactors (F) giving rotation in the forward direction, i. e., when grinding and (R) There will also be accelerating contactors and starting resistance with standard arrangements for operation in correct sequence, but these are not shown except 9, representing the last accelerating contactor to close. This is shown since an interlock on this contaetor could conveniently be used in the control system described below.

The feed motor armature circuit is shown connected to bus bars 23, which will usually .be a variable voltage supply controlled 1 limit relay 15. The time limit relay is indicated as of the thermal type which is con- I nected to be set in operation when the reverse connections for the feed motor are established to automatically interrupt these connections after a definite time interval. The control circuit for the feed motor is. taken through a stop button 12 and a low voltage relay 16 which is closed only if the main motor is energized through switch 24 to ensure that the feed motor is not started with the stone stationary.

The charge-over switch is shown at 17 and limit switches at 18 and 19' and when these are in circuit a push button 20 is provided for reverse running, andinch button 21 fonfine control over the 'magazine casing when lowering the last few inches into position.

The operation is as follows 7 Assume normal grinding is required, i. e., the switch 17 is in its up throw. Button 11. is pressed energizing coil of pilot contactor 10 through 16, 12, 11 and 14. On 10 closing and being retained through its own contacts the forward contactors F are energized through relay 13, (set low to protect the stones) 17 off position interlock 25 on R and relay 1 1. The reverse contactors It cannot close as their circuit is broken by the button 11. Should the relay 13 trip it will open contactors F which in turn will close contactors R through 16, 12, 10, 11, time limit relay 15, 17, interlock 26 on F and relay 14 (set high as explained above). After any predetermined time interval covered by the range of the relay 15, its contacts will open and in so doing open the contactors R, and contactor 1* will now close again through the circuit previously described. Relays 13 and 14. are self-resetting by gravity, but the relay 15 is reset by means of a coil 22 energized through interlock 27 of contactor F, and the interlock on con tactor '9. Relay 15 is self-retaining when reset and therefore coil 22 can now be deenergized and this is done by the opening of the interlock on contactor 9 when contactor 9 closes. 1

The above sequence of events occurs every time relay 13 trips and the equipment requires no manual operation unless relay 14 trips, which means that the feed motors are not powerful enough to clear the jam in the magazine, when working up to the limit set by the relay and in such extreme circumstances hand control is advisable.

The operation for stone inspection or changing would be as follows:-

Switch 17; would be thrown ever to its down position, with the feed. motor rest.

When the casing is ready for lowering button 11 would be pressedclosing the pilot cont-actor, and the forward contactors F through 16, 12, 10, 18, 17, 25 and 14. F

will be retained through 10 and the motor will run until shut down by limit switch 18 which would be arranged to operate a few inches short of the full travel of the casing. The final adjustment for bolting up would then be made by means of the push button 21, which only allows the feed motor to run while it is depressed.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. In combination, a feed mechanism for a grinder or the like, a motor for driving said mechanism, and electroresponsive means governed in accordance with the load on said motor for automatically governing the direction of operation of said motor to regulate the feed of the grinder. 2. In combination, a feed mechanism for a grinder or the like, a motor for driving said mechanism, directional switch mechameans governed in accordance with the load on said motor for automatically eiiectingoperationof said switch mechanism to reverse the direction of operation of said motor and said feed mechanism, the said means including mechanism whereby the extent of the reverse operation of said motor and feed mechanism is automatically limited.

3. In combination, a feed mechanism for a grinder or the like, a feed motor for driving said mechanism, electroresponsive means governed in accordance with the load on said motor for automatically reversing the direction of operation of said motor and said feed mechanism, and a time interval device set in operation when the feed motor is reversed for automatically limiting the extent of operation of the feed motor and feed mechanism in the reverse direction.

4. In combination, a feed mechanism for a grinder or the like, a motor for driving said mechanism, means responsive to the current taken by said motor, directional switch mechanism for controlling said motor, and connections through which said means automatically governs said switch mechanism to automatically reverse the direction of operation of said motor and said'feed mechanism for a limited extent or" operation and to automatically stop said motor in case the current taken thereby in said reversed direction of operation exceeds a predetermined vaiue.

5. In combination, a; feed mechanism for a grinder or the like, a motor for driving the feed mechanism, reversing switch mechanism for said motor, a relay responsive to the 5 current taken by said motor, a time element device, and connections through which said relay governs said switch mechanism to reverse the direction of operation of said motor and said feed mechanism and set said device in operation to limit the extent of said re- 10 verse operation.

In witness whereof, I have hereunto set my hand this 11th day of January, 1927.

RALPH D. GIVEN. 

